Extrusion dies or extrusion heads of the aforedescribed construction are provided in extruder apparatus for producing tubes, pipes and other hollow articles, or as the heads from which an expandable tubular strand of the plastically deformable material can emerge, e.g. for film or foil blowing. The feed means can include a distribution device, for example distribution passages, an annular manifold or the like. The source of the thermoplastified synthetic resin is usually a worm or screw extruder or the like.
In conventional extrusion heads of the type with which the invention is concerned, for example those described in DE-OS 23 06 834 and DE-PS 25 09 024, the feed unit includes distribution passages by means of which the thermoplastified synthetic resin, optionally through a widening annular distribution chamber, enters the annular extrusion gap. This construction results in a microtexturing in the finished product which has been found to be detrimental to the quality thereof.
To suppress this microtexturing, it has been found to be advantageous to incorporate in the distribution passages of the die or head, mixing elements or baffles which direct the inner flow streams outwardly and the outer flow streams inwardly. Such arrangements are costly and require significant maintenance and are not always satisfactory as to the results obtained.